The present invention relates generally to methods and apparatus for measuring certain qualities of reclosable thermoplastic zippered bags.
In particular, the present invention is concerned with reclosable thermoplastic zippered bags of the type described in commonly-assigned copending application Ser. No. 07/531,951, now issued as U.S. Pat. No. 5,070,584 (the '584 patent), such patent being hereby incorporated herein by reference.
The bags described in the '584 patent and described in much more abbreviated fashion below provide confirmation of their closure by producing a distinctive tactile and/or audible indication of the interlocking of the male and female profiles in their zippers. This tactile and/or audible indication of the proper interlocking of the male and female profiles is produced by varying the closure force required to interlock the male and female profiles over the length of the zipper. Typically the closure force is cycled intermittently over the length of the zipper between a low closure force and a high closure force, with the changes in closure force being produced in turn by making one or both of the profiles intermittently structurally discontinuous. These intermittent structural discontinuities are manifest in the form of first and second differently-shaped segments over the length of a profile part interlockable with the opposing profile. The differently-shaped segments interlock differently with corresponding portions of the opposing profile and implicate different closure forces.
The degree of certainty or assurance of closure given by the zippers in such bags is consequently directly correlated to whether perceptible variations in closure force are produced over the lengths of the zippers, but previously no devices or methods were known which could consistently measure whether certain minimum acceptable variations in closure forces were produced in the zippers. Such devices and methods would be useful from a quality control perspective for ensuring that the bags of the '584 patent provide the confirmation of closure sought by users of reclosable thermoplastic bags generally.
Such devices and methods would also be useful, however, for making measurements of the forces required to close or zip a zipper in reclosable thermoplastic zippered bags generally, since the magnitude of force required to interlock the male and female profiles of a zippered bag is also of some importance to consumers.